This invention relates to transporting and positioning of small articles and, in particular, to a pick and place assembly capable of multi-axial motion.
Assemblies for transporting and positioning articles and components of various articles are used in various applications. For example, in a semiconductor industry, these assemblies are used to transport semi-conductor chips from one location to another. In most applications, particularly in the electronics and semiconductor manufacturing industries, high speed and precision of the pick and place assemblies are essential. In particular, a pick and place assembly must be able to transport the articles from one place to another at high speed without damaging the article and to position the article with very high-precision at its destination.
Conventional pick and place assemblies typically employ a pick and place head installed and traveling on a gantry. The pick and place head includes a hollow cylindrical spindle coupled with a vacuum delivery system at one end and a vacuum cup at its other end. Vacuum delivered through the spindle to the vacuum cup by the vacuum delivery system enables the cup to pick up, or collect, an article to be transported. The spindle is also coupled to a driving means for linearly moving the spindle along a Z-axis so as to allow the vacuum cup to approach the article so as to pick it up and to withdraw after placing the article. The spindle may also be coupled to a second driving means which rotates the spindle, i.e. θ-motion, so as to properly position the article before being placed at its destination.
In order to create linear and rotary motions of the spindle, conventional pick and place heads have employed ball screw drives, pneumatic cylinder drives or linear motors. In addition, to account for the axial and rotary motions of the spindle, the conventional vacuum delivery systems have typically employed coiled or looped tubing and rotating union fittings.
Conventional pick and place assemblies suffer from a number of disadvantages, including excessive size and weight, programming and control problems and premature failure. In particular, ball screw drives used in conventional pick and place assemblies to create the linear and/or rotary motions of the spindle considerably add to the excessive size of the assemblies, while the linear motors significantly increase the weight of the pick and place assemblies, making such assemblies difficult to install and move on the gantry. The pneumatic cylinder drives, also commonly used for driving the spindle of the pick and place head, are often difficult to program and control. Moreover, the axial and rotary movement of the spindle in a conventional pick and place assembly often causes a collapse or cracking of the tubing providing the vacuum and a premature failure of the vacuum delivery system.
Another problem experienced by conventional pick and place assemblies is a descent, or free fall, of the spindle if power failure occurs. Such free fall of the spindle can result in damage to the spindle and other parts of the pick and place assembly, requiring costly repairs.
All of the above disadvantages have a significant effect on the speed, accuracy and the operating life of the conventional pick and place assemblies. It is therefore an object of the present invention to provide a pick and place assembly which integrates linear and rotary motions in a compact unit which can be easily mounted on the conventional gantry.
It is a further object of the present invention to provide a pick and place assembly with an improved vacuum delivery system which does not require coiled or looped tubing.
It is a further object of the present invention to provide a pick and place assembly which provides protection against the free fall of the spindle in cases of power failure.